Reduction and oxidation (Redox) are defined by the gain and loss of electrons, respectively, both of which affect the structure and function of proteins. Cardiac stress increases reactive oxygen species (ROS), which oxidize proteins, thereby affecting a wide variety of cellular functions, including hypertrophy and cell death. Thioredoxin1 (Trx1) is a 12 kD protein that protects the heart from pathological hypertrophy and ischemia/reperfusion. Trx1 interacts with intracellular signaling molecules, and reduces oxidized cysteine residues, thereby modulating their function. Our long-term goal is to identify important substrates of Trx1 in the heart and elucidate the functional significance of the regulatory effect of Trx1 in response to clinically relevant stress. In order to identify novel targets of Trx1 durin myocardial ischemia, we generated transgenic mice with cardiac specific expression of a Trx1 trap mutant. One of the proteins we identified using this system was AMP-activated protein kinase (AMPK), a serine threonine kinase. AMPK is an important sensor of energy stress and positively regulates the catabolic process to maintain the energy level. We hypothesize that AMPK is subjected to cysteine oxidation during myocardial ischemia, which negatively regulates AMPK. Trx1 is an essential co-factor of AMPK, allowing AMPK to be activated during myocardial ischemia to promote cell survival by reducing the oxidized cysteines in AMPK. AMPK and Trx1 form a positive feedback loop to stimulate one another's functions during stress. We will: 1) elucidate the molecular mechanism by which cysteine oxidation during ischemia inactivates AMPK, 2) demonstrate the role of Trx1 as an essential co-factor of AMPK during myocardial ischemia, and 3) demonstrate that AMPK and Trx1 form a positive feedback mechanism to protect the heart against ischemia, but that their function is impaired in response to consumption of a high fat diet. We will use proteomic analyses of posttranslational modifications and unique genetically altered mouse models. Our study will elucidate how posttranslational oxidative modification of cysteine residues regulates the activity of AMPK during metabolic stress and show that Trx1 is a critical co-factor of AMPK in the protection of the heart against prolonged ischemia.